Machines for cutting hard surfaces, such as used in the trenching and mining industries and for removing the upper surfaces of concrete and asphalt pavement, employ tools fitted into tool holders on a rotatable wheel or drum. The tools have a tapered forward cutting end and axially located behind the forward cutting end is a cylindrical shank that rotatably fits within a complementarily shaped bore in the tool holder. Between the forward cutting end and the shank, the tools have a rearwardly directed annular surface or flange that contacts the forward surface of the tool holder. Force is applied through the rotating drum or wheel to the tool holder and through the radial flange to the tool to thereby force the tool into the hard surface to be cut.
The shank of the tool is retained in the bore of the tool holder by a sleeve made of a spring steel that fits around the shank of the tool and engages a shoulder on the shank to prevent the shank from being removed from the sleeve. The sleeve is compressed during the insertion of the shank and sleeve into the bore of the tool holder after which the radially outward force applied by the sleeve against the inner wall of the bore retains the shank of the tool within the bore. The radially outwardly directed force applied by the sleeve as it is compressed prior to insertion into the bore of the tool holder also complicates the insertion process.
To receive the tool and compressed sleeve, the bore of the tool holder has a frustoconical countersink, with the outermost diameter of the countersink being larger than the outermost diameter of the unstressed sleeve. To insert the tool into the tool holder, the distal end of the shank is fitted into the bore with the rearward edge of the sleeve abutting the frustoconical surface of the countersink surrounding the bore. Thereafter, the nose of the tool is struck with a hammer or the like, forcing the shank of the tool and the sleeve rearwardly. As the sleeve moves axially into the bore, it is compressed by the frustoconical countersink.
The insertion of the tool into a tool holder require a machine operator to use both hands. In many cases, however, the drum or wheel of the machine is in such an orientation that the tool holder is inaccessible to both hands of the technician without a time consuming repositioning of the drum or the technician's body. It would greatly simplify the insertion of replacement tools in the tool holders of a machine if a technician could position and insert the tool into a tool holder using only one hand.
During the operation of such machines, the useful life of the tools is enhanced by the rotation of the tool, causing it to wear evenly around its circumference. The tools are mounted at an angle of about seven degrees on the drum or wheel and the contact of the tool body with the surface to be cut applies a component of force to the side of the tool that is perpendicular to the axis of rotation. The rotation of the flange of the tool against the forward surface of the tool holder causes wear to the forward surface of the tool holder. To prevent such wear, it has become common to provide an annular wear ring around the shank of the tool between the forward surface of the tool holder and the rearwardly directed flange of the tool.
When the wear ring operates properly, the wear ring remains stationary against the forward surface of the tool holder while the tool rotates against the forward surface of the wear ring such that only the forward surface becomes worn away. Currently existing wear rings are retained in the stationary position by the resistance caused between the forward end of the tool holder and the rearward surface of the wear ring, which is generally greater than the resistance between the forward surface of the wear ring and the rearwardly directed radial flange of the tool. Although this is so, there is a tendency for the wear ring to rotate with respect to the forward end of the tool holder. The same forces that cause the tool body to rotate also cause the wear ring to rotate. Considering that a tool may undergo as many fifty thousand rotations within a single day, the forward end of the tool holder will undergo a significant wear caused by the rotation of the wear ring. To minimize the rotation of a wear ring that is retained by friction between the forward end of the tool holder and the rear surface of the wear ring, it is desirable that the outer diameter of the wear ring be no greater than, or even smaller than, the outer diameter of the radial flange of the tool body. It would be desirable, therefore, to provide a wear ring that is retained against rotation with respect to the tool holder.
Several problems are also encountered in removing the tool from a tool holder. Presently, it is the practice to provide an annular groove around the tapered forward cutting end of the tool that can be grasped by the prongs of an extraction tool. Where a wear ring is fitted around the shank of the tool, the use of existing extraction tools may result in the wear ring falling off the end of the shank of the tool onto the work surface below the machine. As a result, the machine operator may be required to collect the dropped wear rings after the defective tools of the machine have been replaced.
Several efforts have been made to overcome the foregoing problems, and one of the most notable is disclosed by Simon, U.S. Pat. No. 4,818,027. Simon discloses a rotatable tool having an axial shank, a compressible sleeve fitted around the shank, and a wear ring fitted around the compressible sleeve with the inner diameter of the wear ring equal to or less than the diameter of the bore of the tool holder. The shank has a shoulder at the forward end thereof that is spaced from the radial flange, and the forward end of the sleeve abuts against the shoulder. With the sleeve compressed by the wear ring, the distal end of the shank can be more easily fitted into the bore of the tool holder to thereby facilitate the insertion of the shank of the tool. As the shank of the tool is driven deeper and deeper into the bore, the wear ring is forced forwardly off of the forward end of the sleeve after which all the radially outwardly directed forces of the compressed sleeve are applied to the inner surface of the bore to retain the tool in the bore.
Although the device of Simon does assist in the insertion of the shank of the tool into a tool holder, and provides for a wear ring between the forward surface of the tool holder and the rearwardly directed annular surface of the flange, the wear ring is retained against rotation with the tool only by the friction between the forward surface of the tool holder and the rearward surface of the wear ring and therefore rotates with the tool.
There are certain problems that have been found with the structure of the sleeve and wear ring of Simon. The rotation of the shank within the sleeve of Simon requires that the forward edge of the sleeve abut against the annular shoulder that is spaced from the surface of the radial flange. However, it has been found during the use of the tool the sleeve becomes somewhat extruded, causing it to lengthen, and as the sleeve lengthens the forward end thereof is forced over the annular shoulder. The sleeve then becomes pinched between the enlarged diameter portion of the shank adjacent the radial flange and the bore of the tool holder, thereby preventing or inhibiting the rotation of the tool. Where the tool fails to rotate properly, it will become prematurely worn and reduce the efficiency of the machine or require frequent service.
Products currently made in accordance with Simon include a wear ring with an inner diameter equal to the diameter of the bore, and as a result, the distal end of the shank cannot be manually inserted into the bore of a tool holder using one hand. Efforts to provide a wear ring having a central opening that is less than the diameter of the bore to thereby further compress the sleeve until the distal end of the shank and sleeve may be manually fitted within the bore have resulted in an increase in the incidence of wedging between the shank and the bore. This is because the bore of the wear ring must be made smaller than the diameter of the bore of the holder, and since the enlarged portion of the shank must rotate within the bore of the wear ring, the shoulder at the forward end of the shank must be correspondingly reduced.